With the development in OLED display technologies, OLED display panels have been widely used in electronic devices such as mobile phones, tablets, and flat TVs. Compared to conventional liquid crystal display (LCD) devices, OLED display devices do not require backlight. They are also relatively thin and light, and often have a wide viewing angle and short response time. In addition, OLED display devices generally have higher light emission efficiencies.
Often, in an OLED device, the conductive organic layer for emitting light is positioned between the two electrode layers (i.e., the cathode layer and the anode layer) to form a “sandwich” shaped structure. In such an OLED device, holes are injected into the organic layer from the anode and electrons are injected into the organic layer from the cathode. Holes move toward electrons and combine with electrons in the organic layer to form excitons, i.e., a bound state of electron and hole. The decay of the excitons results in relaxation of energy, accompanied by emission of radiation, e.g., visible light.
White light OLED has been used in the OLED devices for their simple operation mechanism and potential for cost reduction. By incorporating color filters (CF) with white OLEDs, three primary colors, red, green, and blue can be realized. In such display panels or devices, the white OLEDs can be used to adjust the gray scale of the units in a display panel, and the lifetimes of the OLEDs for displaying the primary colors (i.e., red, green, and blue) are the same so that color distortion caused by different lifetimes of OLEDs with different colors can be reduced.
Meanwhile, as a human-computer interaction means, touch technology and touch screen technology have developed and matured in the past years. This is triggered by the demand from more and more touch-sensitive devices. Because of advantages such as high signal to noise ratio (SNR) and low cost of production, self-capacitance in-cell touch technology has been a focus point of many researches on touch technology. One kind of self-capacitance is based on measuring the capacitance of a single electrode with respect to ground. When a human finger or a conductive stylus is near the electrodes, the human-body capacitance changes the self-capacitance of the electrode, and the changed capacitance can be sensed by an integrated circuit (IC) connected to the electrode. Among different touch technologies, in-cell touch technology integrates the capacitance sensors within the pixel or sub-pixels of the display panel so that the display panel is not required to be bonded with an additional touch panel as in the conventional touch display panels.
Conventionally, in a self-capacitance touch and display panel, often, cathode is made of indium-tin oxide (ITO). A fixed voltage is applied across the cathode and the anode for display images and responding to touch motions. When a user touches the display panel, capacitance changes at the touched intersections may be sensed by the corresponding control IC. The location of the touch can be determined or mapped by applying various algorithms.
However, a touch sensing pattern is often required to be formed in a patterning process, which may add complexity to the fabricating process and increase the fabricating cost. Further, a touch motion may change the voltage applied on the OLEDs at the touch location and cause the electric current flowing through the OLEDs to change or fluctuate. As a result, the electric current flowing through the OLEDs on a display panel may not be stable or uniform when a human finger or a conductive stylus touches the display panel. Also, conventional ITO electrodes may have high resistivity and may slow down the responses to the touch motion.